(a) Technical Field
The present disclosure relates, generally, to a DC-DC converter. More particularly, it relates to an emergency control apparatus and method which maintains the operation state of an electric vehicle such as a hybrid vehicle in the event of failure of a bidirectional DC-DC converter connected between a battery as a power source and an inverter for operating a drive motor.
(b) Background Art
A hybrid vehicle, in the broad sense, means a vehicle that is driven by efficiently combining at least two different types of power sources. In most cases, the hybrid vehicle is driven by an engine which generates a rotational force by burning fuel (e.g., fossil fuel such as gasoline) and an electric motor which generates a rotational force with electric power of a battery. Such a hybrid vehicle is typically referred to as a hybrid electric vehicle (HEV).
The hybrid vehicle is a vehicle of the future which can improve fuel efficiency and reduce exhaust gas by employing the electric motor as an auxiliary power source as well as the engine as a main power source. Extensive research has been conducted to improve fuel efficiency and develop environment-friendly products.
The hybrid vehicle is driven in an electric vehicle (EV) mode, which is directed to a pure electric vehicle mode using only the power of the electric motor (or drive motor), in a hybrid electric vehicle (HEV) mode, which is an auxiliary mode using the rotational force of the drive motor as an auxiliary power source with the use of the rotational force of the engine as a main power source, or in a regenerative braking (RB) mode, in which braking energy or inertia energy of the vehicle produced by braking or during driving by inertia is recovered by power generation of the drive motor and charged in a battery.
Accordingly, the mechanical energy of the engine and the electrical energy of the battery are used together, the engine and the drive motor are operated in their optimal operation regions, and the braking energy is suitably recovered by the drive motor during braking. As a result, it is possible to improve the fuel efficiency of the vehicle and effectively use the energy.
A hybrid vehicle typically includes a battery, which repeats charge and discharge during operation of the vehicle to supply electric power required for driving the drive motor, and an inverter for rotating the drive motor by the power of the battery.
The battery supplies require electric power and is charged with electric power generated by the drive motor during regenerative braking, and the inverter inverts the phase of the electric power supplied from the battery to operate the drive motor.
Recently, a DC-DC boost-buck converter (e.g., high voltage DC-DC converter, HDC) for bidirectional power conversion has been connected between the battery and the inverter to suitably improve the performance of the hybrid vehicle. The use of this bidirectional DC-DC converter is a major trend in the hybrid vehicle industry.
Japanese Patent Publication No. 2003-134606, incorporated by reference in its entirety herein, is directed to a technique in which a bidirectional DC-DC converter is suitably connected between a battery and an inverter in a vehicle driven by a drive motor.
FIG. 1 is a schematic diagram of a power conversion configuration of a typical hybrid vehicle, in which a circuit configuration of a bidirectional DC-DC converter 20 and a connection state of a battery 10, the converter 20, inverters 31 and 32, and drive motors 33 and 34 are shown, in which the two drive motors 33 and 34 are suitably driven by the two inverters 31 and 22.
As shown in the figure, the DC-DC converter 20 preferably includes switching elements Q1 and Q2 such as transistors for controlling the power supply, diodes D1 and D2, and an inductor 21. Preferably, the switching elements Q1 and Q2 are switched on and off by control signals applied from a controller (not shown) to form a current flow path through the diodes D1 and D2, thus performing the function of supplying electric power from the inverters 31 and 32 to the battery 10 (buck operation) and the function of supplying electric power from the battery 10 to the inverters 31 and 32 (boost operation).
Accordingly the switching element Q1 and the diode D2 performs the function of supplying electric power from the inverters 31 and 32 to the battery 10 and the switching element Q2 and the diode D1 performs the function of supplying electric power from the battery 10 to the inverters 31 and 32.
Accordingly, the transistor Q1 and the diode D2 are referred to as “buck switching elements”, and the transistor Q2 and the diode D1 are referred to as “boost switching elements”.
The DC-DC converter 20 is suitably connected between the battery 10 and the inverters 31 and 32 converts the power from the battery 10 according to the output (operation/generation) of the drive motors 33 and 34 and supplies the converted power to the inverters 31 and 32 while a main relay 11 is turned on. Alternatively, the DC-DC converter 20 suitably converts the power (generated by the drive motors during regenerative braking) from the inverters 31 and 32 and charges the battery 10.
However, although the DC-DC converter plays an important role in the performance of the hybrid vehicle, the power conversion flow is stopped in the event of failure of the DC-DC converter, which causes serious problems such as complete discharge of the battery, discontinuation of vehicle operation, occurrence of safety accidents, etc.
That is, while the DC-DC converter operates normally, the above-described power conversion flow is suitably smooth. However, in the event that the operation of the DC-DC converter is cut off due to failure, the state of charge (SOC) of the battery may be suitably lowered, and it may have an effect on the driving performance of the vehicle (e.g., regenerative braking is impossible) and, further, the operation of the vehicle may be discontinued.
FIGS. 2 and 4 are diagrams illustrating certain problems which may occur in the prior art structure.
FIG. 2 is a diagram showing an example where the entire power module in the converter 20 is out of order. For example, when a failure occurs while all of the switching elements Q1 and Q2 and the diodes D1 and D2 are open, the power flow path between the battery 10 and the inverters 31 and 32 is completely interrupted, and as a result, the engine start-up using the inverter, the pure electric vehicle (EV) mode, and the hybrid electric vehicle (HEV) mode are all disabled. Accordingly, the operation of the hybrid vehicle is discontinued and, when a failure occurs during high speed driving, it may lead to a serious accident.
FIG. 3 is a diagram showing an example where the buck switching elements Q1 is out of order. When a failure occurs while the buck switching element Q1 is open, the power flow path from the battery 10 to the inverters 31 and 32 is maintained; however, the power flow path from the inverters 31 and 32 to the battery 10 is interrupted. Accordingly, the power of the battery is gradually exhausted, and it may lead to a situation in which the battery is completely discharged. In the worst case, the entire battery should be replaced. Moreover, since the regenerative braking or generation operation of the vehicle is completely cut off, the driving performance of the vehicle is considerably reduced.
FIG. 4 is a diagram showing an example where the inductor is out of order. When the coil of the inductor is suitably disconnected, the entire power flow path between the battery 10 and the inverters 31 and 32 is interrupted in the same manner as the failure of the entire inverter power module, which may lead to the same result as FIG. 2.
In the prior art power conversion structures (e.g., Japanese Patent Publication No. 2003-134606, incorporated by reference in its entirety herein), in which the DC-DC converter 20 is used in the above-described manner, it is impossible to solve various problems which may occur in the event of failure of the DC-DC-converter 20. Accordingly, it is necessary to provide a method for maintaining the power flow path between the battery and the inverters even in the event of failure of the DC-DC converter.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.